This invention relates to a contactless power supply system, with inductive wires along a traveling path of a moving object. The inductive wires operate at a predetermined frequency under an alternating current (AC) power supply. The moving object has a built-in power inducing coil coupled to the inductive wires. The power inducing coil in the moving object induces energy for supplying to a power consuming load.
An example of a conventional contactless power supply system, comprises a power supply device limiting current into inductive wires to a fixed current value, as disclosed in Japan publication No. 10-174206.
The power supply device cited comprises, a current converter powered by the inductive wires outputting a fixed high frequency current, a control amplifier controlling the current (wire current) to the inductive wires, a pulse width modulation (PWM) circuit acting as a switching device regulating wire current and frequency with the output value of the controller amplifier, and a gate driving circuit. The power supply device with an equivalent circuit employs the wire current value as the control decision current. Moreover, capacitors connected in parallel to the power supply rails result in a resonant circuit.
However, in the conventional contactless power supply system, the inductive wires provide minimal impedance, hence the load fluctuation in the inductive wires produces a significant change in the wire current. As load decreases and the current varies significantly, the control decision current may diverge to an uncontrollable degree.